Signal Bleed - inductive clam

Hey guys.... been a while. I've been locating past 6 months with a contractor to local Telcom. Been going well. We use the Telcom mapping system which sucks so bad, they need us to go and not only pinpoint, but validate and correct their info when there is a dig in the area. Often lines have not been reported in their system and we find all kinds of stuff. Or opposite, line has been cut or defunct, even pole removed, yet they still show line in area. Or the one I love, overhead lines in trenches. Yup... thats how bad their system is. But it keeps us employed.

Looking for input on signal transferring to other lines in congested areas or common ducts, pole-drops, manholes etc... when clamped. Wondering if better ways to avoid it.

Two things:

1. At the clamp itself, since it is actually induction and not direct connect, I would imagine there is always some signal bleed from the clamp itself that even though attached to one line, will drift over to adjacent lines. Often lines are in bundles on a pole and are fairly taught. Can separate enough to get clamp around one, but back of clamp touching the next line. I use a 5" clamp. MetroTech brand. Would a smaller clamp make a difference to how directed the signal is and how much bleeds off?

We have two main telcoms in our area and often lines side by side. Gladly I have been able to deduce the correct signal if I pick up more than one, but is time consuming verifying against other evidences such as our own manholes, building connections, etc.

2. Side by side lines in a duct or pilaster / pole-drop. So lets say I can isolate a line at a good distance from other lines at the clamp point. But then line eventually works its way into a duct shared with other line. Naturally some signal will be shared with the non-target line. Any way to improve on this? Frequencies? Clamp size, other methods?

Re: Signal Bleed - inductive clam

Vivax and radiodetection both sell a signal direction attachment (but you must have one of their locators and transmitter) they work well to identify the correct line. And there is a special radiodetection SD (signal direction) inductive clamp that would be good for you.

Signal Bleed ~ Inductive Clamp

Originally Posted by RanVan

Hey guys.... I'm looking for input on signal transferring to other lines in congested areas or common ducts, pole-drops, manholes etc... when clamped. Wondering if better ways to avoid it. I use a 5" clamp. MetroTech brand.

Greetings RanVan! I have been a utility locator for USIC for 20 years. My area is loaded with risers on utility poles, utility handholes, TV & At&T multi-conduit duct banks and manholes filled with laterals.

My mainline equipment is Radio Detection 8000 (RD 8000). I use my RD 8000 inductive clamp many times daily. I have never used a MetroTech so I don't know what to expect when clamping a utility using your set-up.

The RD 8000 has many induction frequencies. F8 is the least powerful induction frequency in the line-up, f33 is next in line, f65 @ 3rd in power and many more thereafter. The first I have listed are the three frequencies I have ever used. For no particular reason, I favor frequency 33 when I use my inductive clamp. Whenever I suspect a bleed-off is possible to another utility when I perform my initial sweep, I will step back to frequency 8 with great success.

I checked out the MetroTech operations manual on line and I could not find a list of your available frequencies there. I YouTubed the MetroTech training video and it was no help on your frequencies available. These MetroTech YouTube training videos I found are weak on how to properly perform an induction clamp locate; sweeps and frequencies. Check out 9:00 on this video:

Re: Signal Bleed ~ Inductive Clamp

Thanks Wingfoot... my metrotech gear can be set to several frequencies on inductive clamp mode. Tx automatically detects that inductiive clamp is connected and allows you to scroll through range of frequencies.... and receiver as well. Receiver in fact has like 30+ frequencies... more than I have ever needed so far.

Will follow up in the field on your suggestions and let you know how it goes. Thanks so much again for the detailed response.

Re: Signal Bleed - inductive clam

Interestingly.... on the vid you posted, they suggest using smallest clamp possible that will fit the target line you are clamping. Hmmmmm..... will see if my supplier will let me demo some various clamps other than my 5". Metrotech offers a 3" for sure, maybe less. Certainly bigger but I don't need.

I really should have a backup anyway. No such thing in our area as a 5" + bundle to clamp anyway. Only time I use the full width is if I have to clamp around a duct... which is seldom. But again, wonder if getting too close to other lines. Even the back of the clamp will emit some signal.

Was on a site other day and was distracted connecting my clamp to feed line of a tel pedestal. Left it sitting on ground maybe an inch from line. Still got some signal in the line about 150' away. Scratched my head why signal sucked so bad.... went back to Tx and found my mistake. Clamped on properly and was perfect signal, perfect locate.

Point though was that I still got some amount of signal when clamp was couple inches away from line and not clamped around it. So must be emitting. It is induction after all.